In general, transmissions are used for transferring rotary force of an engine or motor to a driving wheel according to a gradient state of a road or driver's will.
The transmissions may be classified into a manual transmission that directly selects a shift level upon the driver's will, an automatic transmission in which shifting is automatically made according to a driving condition of a vehicle, a continuously variable transmission (CVT) in which the shifting continuously varies without a shift area between the shift levels, and the like.
Among, the CVT includes a driving pulley mounted on an input shaft connected with the engine or motor, a driven pulley mounted on an output shaft, and a belt connecting the driving pulley and the driven pulley and operates in such a manner that the shifting is made while an outer diameter of the belt varies with movement of the pulley.
As one of the existing continuously variable transmission, Korean Patent Registration No. 10-1351073 (Jan. 22, 2014) discloses contents regarding a continuously variable transmission in which slots which cross each other are formed on two disks disposed to face each other, respectively and the outer diameter of the driving belt is changed by a sliding pin which moves in a radial direction of the disk while being accommodated in each slot with relative rotation of the respective disks to control an RPM between the driving pulley and the driven pulley.
Moreover, in the existing continuously variable transmission, a spiral spline is formed on a separate movable shaft and a spline groove is formed at a coupling portion of the disk, so as to change the radius of the sliding pin by relatively rotating two disks.
However, in the related art, the relative rotation between the disks is implemented in a spline method by linear movement of the movable shaft, a linear movement section of the movable shaft needs to be particularly secured, and as a result, a structure becomes complicated and it is difficult to manufacture a device in a small size.
Further, since the existing continuously variable transmission uses a rotation method using the spline, rapid and accurate shift control is difficult.
As a result, in recent years, various researches into the continuously variable transmission which can simplify the structure and contribute to miniaturization and is used for rapidly and accurately the shift control have been made, but has not yet been insufficient. Therefore, the development of the corresponding continuously variable transmission has been acutely required.